Image elimination apparatus, image eliminating method and image forming apparatus

ABSTRACT

An image elimination apparatus includes a first reader configured to read a status of a sheet, a first judgment portion configured to judge whether the read sheet is reusable or not, an image eliminator configured to eliminate an image formed on the sheet, a second reader configured to read the sheet passing through the image eliminator, a second judgment portion configured to judge whether the image formed on the sheet is eliminated or not, and a controller configured to control the first reader and the second reader so as to read with different reading precision.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromthe prior U.S. Patent Application No. 61/112,649, filed on Nov. 7, 2008and Japanese Patent Application No. 2009-176054, filed on Jul. 29, 2009;the entire contents of all of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to an image elimination apparatus foreliminating an image from a sheet with the image formed and enablingreuse of the sheet, an image eliminating method, and an image formingapparatus.

BACKGROUND OF THE INVENTION

In recent years, from the standpoint of resource usage by recycle, thereis an increasing demand for an image forming and eliminating apparatusfor enabling elimination of an image from a sheet with the image formedand reuse of the sheet. An apparatus for eliminating an image from asheet with the image formed is disclosed in, for example, JapanesePatent Application Publication No. 8-6446.

However, even if the image is eliminated, whether the sheet itself withthe image formed can be reused or not is not clear. Furthermore, afterelimination, whether the image on the sheet is eliminated or not isunknown.

SUMMARY OF THE INVENTION

The present invention is intended to provide an image eliminationapparatus having a function for judging whether a sheet intended to bereused is reusable or not, an image eliminating method, and an imageforming apparatus.

To achieve the above advantage, the aspect of the present invention isto proved an image elimination apparatus comprising a first readerconfigured to read the status of a sheet, a first judgment portionconfigured to judge whether the read sheet is reusable or not, an imageeliminator configured to eliminate the image formed on the sheet, asecond reader configured to read the sheet passing through the imageeliminator, a second judgment portion configured to judge whether theimage formed on the sheet is eliminated or not, and a controllerconfigured to controlling the first reader and the second reader so asto read with different reading precision.

To achieve the above advantage, the aspect of the present invention isto proved an image eliminating method comprising reading a status of asheet and first judging whether the sheet is reusable or not,eliminating the image formed on the sheet, and second judging whetherthe image is eliminated at the eliminating or not, wherein readingprecision at the first judging and reading precision at the secondjudging are different from each other.

To achieve the above advantage, the aspect of the present invention isto proved an image forming apparatus comprising an image forming portionconfigured to form an image on a sheet and an image eliminationapparatus configured to eliminate the image on the sheet formed by theimage forming portion, wherein the image elimination apparatus includesa first reader configured to read the status of a sheet, a firstjudgment portion configured to judge whether the read sheet is reusableor not, an image eliminator configured to eliminate the image formed onthe sheet, a second reader configured to read the sheet passing throughthe image eliminator, a second judgment portion configured to judgewhether the image formed on the sheet is eliminated or not, and acontroller configured to control the first reader and the second readerso as to read with different reading precision.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of the image forming apparatus ofthe first embodiment;

FIG. 2 is a schematic view of the image elimination apparatus of thefirst embodiment;

FIG. 3 is a block diagram showing a system including the imageelimination apparatus and image forming apparatus of the firstembodiment;

FIG. 4 is a flow chart showing the process of the first embodiment;

FIG. 5 is a flow chart showing the process of the first embodiment;

FIG. 6 is a flow chart showing the process of the second embodiment;

FIG. 7 is a flow chart showing the process of the second embodiment;

FIG. 8 is a schematic view of the image elimination apparatus of thethird embodiment;

FIG. 9 is a flow chart showing the process of the fourth embodiment;

FIG. 10 is a flow chart showing the process of the fourth embodiment;

FIG. 11 is a schematic view of the image elimination apparatus of thefifth embodiment;

FIG. 12 is a schematic view of the reader and image eliminator of theimage elimination apparatus of the sixth embodiment;

FIG. 13 is a schematic view of the reader and image eliminator of theimage elimination apparatus of the sixth embodiment; and

FIG. 14 is a schematic view of the reader and image eliminator of theimage elimination apparatus of the sixth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the first embodiment of the present invention will beexplained with reference to FIGS. 1 to 5.

FIG. 1 is a schematic view of the image forming apparatus (hereinafter,abbreviated to MFP) 1 to which a post-processing device 3 having abuilt-in image elimination apparatus 2 of the present invention and FIG.2 is an enlarged schematic view of the image elimination apparatus 2.

The MFP 1 forms an image on sheets supplied from a sheet cassette 4 andfeeds the image-formed sheets to the post-processing device 3. The MFP1, according to the user input to a control panel 5, on the sheets whichare supplied one by one from the sheet cassette 4, forms the image by animage forming portion 6, for example, by an electrostatic photographicrecording system. Further, the MFP 1, using ink or toner using acoloring material which is achromatized by applying heat higher than acertain temperature for a predetermined period of time, forms the imageon the sheets. The post-processing device 3, for example, sorts orstables the sheets with the image formed by the MFP 1.

The image elimination apparatus 2 includes a sheet supply tray 7, areader 9 and an image eliminator 10 which are installed along a firstsheet conveying path 8, a stack box 11 installed to abolish sheetsjudged as nonreusable, and a discharge port 12 for feeding sheets to theMFP 1.

On the sheet supply tray 7, the sheets with the image formed arestacked. The reader 9 has a CCD sensor 13. The CCD sensor 13, asdescribed later, to judge whether the sheets are usable or not and theprint of the sheets is eliminated or not, reads the surface of each ofthe sheets. The image eliminator 10 has internally a heater 14 andeliminates the image printed on the sheets by heat. On the first sheetconveying path 8, a plurality of rollers 15 are installed and the sheetsare conveyed by the plurality of rollers 15. Further, on the first sheetconveying path 8, a first flapper 16 and a second flapper 17 areinstalled. The first flapper 16 separates the sheets judged asnonreusable from the first sheet conveying path 8. The sheets separatedby the first flapper 16 are guided to the stack box 11. Between thefirst flapper 16 and the stack box 11, a first sensor 26 is installed.The second flapper 17 is installed immediately before the discharge port12 to the MFP 1 and guides the sheets to a second sheet conveying path18 for conveying again the sheets with the image eliminated by the imageeliminator 10 to the reader 9. Also on the second sheet conveying path18, the plurality of rollers 15 for conveying sheets are installed. Onthe image elimination apparatus 2, a pick-up roller for taking outsheets one by one from the sheet supply tray 7 and feeding the sheets tothe first sheet conveying path 8 is installed. Between the secondflapper 17 and the discharge port 12, a second sensor 27 is installed.

FIG. 3 is a block diagram showing the electrical connection of the imageelimination apparatus 2. To a CPU 19, via a system bus 20, a ROM 21, aRAM 22, the CCD sensor 13 of the reader 9, the heater 14 of the imageeliminator 10, a flapper driver 23 for controlling the first flapper 16and second flapper 17, a sheet conveying motor 24, a sheet supply motor25, and a sensor driver 28 for controlling the first sensor 26 andsecond sensor 27. Further, the CPU 19 communicates with the MFP 1 by aninterface 29 connected via the system bus 20. In the ROM 21, a programfor operating the CPU 19, a density threshold value used to decide thefold depth of sheets, a density threshold value for checking whether theimage is eliminated from the sheets or not, and data of the print rateof the sheets which is an index of usable or unusable are stored. In theRAM 22, the highest density of the image obtained when reading thestatus of a sheet and the position information indicating the highestdensity are stored. The CCD sensor 13 is arranged as a row of linesensors and detects the color shade of sheet. The heater 14 uses an IHheater and while the sheet passes through the image eliminator 10,applies heat to the sheet and achromatizes the coloring material. TheCPU 19 drives respectively the first flapper 16 and second flapper 17via the flapper driver 23 and separates the sheet from the first sheetconveying path 8.

FIGS. 4 and 5 are a flow chart showing the flow of the program stored inthe ROM 21. Firstly, a user instructs image elimination of the sheet puton the sheet supply tray 7 from the control panel 5 (30). Then, the CPU19 receives an elimination command from the MFP 1 via the interface 29(31), in order to read the status of the sheet and eliminate surely theimage from the sheet, sets the sheet conveying speed to a first speed(32), drives the heater 14 of the image elimination apparatus 2 (33),and drives the sheet conveying motor 24 (34). Next, the CPU 19 drivesthe sheet supply motor 25 (35), picks up one sheet from the sheetsstacked on the sheet supply tray 7, and feeds the sheet to the firstsheet conveying path 8.

The sheet fed to the first sheet conveying path 8 is guided to thereader 9 by the rollers 15. At the point of time when the leading edgeof the sheet reaches the reader 9, the CCD sensor 13 of the reader 9starts reading (36), during passing of the sheet through the CCD sensor13, reads the image on the sheet surface, and judges whether the sheetis usable or not (37). Hereinafter, an operation of reading the statusof a sheet to judge the possibility of reuse such as existence ofcreases and corner folds of the sheet or a high print rate is referredto as first reading. If the first reading finds creases of the sheet orcorner folds thereof or that the print rate is high, thus elimination isdifficult, the sheet is judged as unusable. And, the CPU 19 drives thefirst flapper 16 (38), guides the sheet to the stack box 11, and whenjudging that the sheet passes through the first sensor 26 installed atthe entrance of the stack box 11 (39), finishes the elimination process(40). Further, in the case of the first reading, to store the highestdensity data and the position data indicating the density in the RAM 22and in the case of reading to be executed after elimination of the imagewhich will be described later, use the stored data is possible. Thehighest density is referred to as integration of either or both of thehighest value of the print rate in divided several regions of the sheetand the highest value of the output of the CCD sensor 13. The highestdensity is used in comparison of the density read by the reader 9 withthe threshold value stored beforehand in the ROM 21.

A sheet having corner folds may cause sheet jamming to the apparatus.The sheet having creases, due to the roughness of the sheet surfaceowing to creases, may cause variations in adhesion of toner and ink. Adeeply folded sheet may also cause variations in toner adhesion.Therefore, the CPU 19, to avoid a mechanical failure and a defectiveimage quality, judges the sheet having creases or corner folds asnonreusable.

To a sheet judged as reusable by the first reading, that is, acrease-free sheet or a low-print-rate sheet, the image eliminator 10applies heat by the heater 14 and eliminates the image. Hereafter, theCPU 19 drives the second flapper 17 (41) and guides the sheet passingthrough the image eliminator 10 to the first sheet conveying path 8 onthe upstream side of the reader 9 via the second sheet conveying path18. Next, the CPU 19 sets the sheet conveying speed to a second speedhigher than the first speed used when executing the first reading andimage elimination (42), permits again the CCD sensor 13 of the reader 9to read and pass the pixels, and checks whether the image is eliminatedor not (43). Hereinafter, to read an image on a sheet by the CCD sensor13 to check whether the image is eliminated or not is referred to assecond reading. As the sheet conveying speed is increased, reading ofthe pixels becomes rough. Therefore, as the conveying speed when thesheet passes through the reader 9 is increased, the reading precision islowered. Further, when executing the first reading, among the imageformed on the sheet, the position data indicating the highest density isstored in the RAM 22 and when executing the second reading, only theposition indicating the highest density stored in RAM 22 and theperiphery thereof are read and that the image is eliminated at theposition can be judged, so that that the entire image of the sheet iseliminated can be decided.

Here, the reason that the first reading precision is made higher thanthe second reading precision will be explained. As described before, atthe time of the first reading, to read creases and corner folds of thesheet and the highest density and judge the possibility of reuse of thesheet is an object. The image elimination apparatus 2 itself cannotpredict beforehand the location of creases or corner folds and thelocation indicating the highest density, and the density obtained fromthe part of creases or corner folds and the pattern shape thereof areusually irregular, and the contrast of the part of creases or cornerfolds is lower than that of the part with an image of characters formed.In order to judge existence of creases or corner folds, to read theentire sheet with such precision as to recognize the density, patternshape, and contrast and reserve the processing time for judging thecreases or corner folds is necessary. Therefore, to switch the sheetconveying speed to a considerably slow speed (for example, inconsideration of perfect image elimination by the image eliminator 10following the first reading, about 21 cm, which is the length of anA4-sized sheet in the lateral direction, per minute) is desired. Asmentioned above, the first reading precision can be read at theconveying speed at the time of sheet elimination, so that as a result,the reading precision is improved extremely. On the other hand, in thesecond reading, that effective elimination of the image can be evenrecognized is desirable. For example, if the elimination object is adocument image, the image is arranged almost regularly, so that there isno need to recognize as far as the density pattern shape and even if theimage is read at such a speed as recognizing existence of the image,there are few problems imposed. Furthermore, the image elimination isexecuted for the entire sheet by taking time, so that if the eliminationof the image at the location showing the highest density can be evenrecognized, that other images are also eliminated may be assumed.

In the second reading, when there exists a pixel indicating apredetermined density or higher on a sheet and that the image is noteliminated is judged, in order to drive the first flapper 16 and abolishthe sheet, the CPU 19 guides the sheet to the stack box 11 and whenjudging that the sheet passes through the first sensor 26, finishes theprocess (40). At 43, there exists no pixel indicating the predetermineddensity or higher on the sheet and when judging that the image iseliminated, the CPU 19 returns the second flapper 17 (44) and guides thesheet from the discharge port 12 into the MFP 1. When judging that thesheet passes through the second sensor 27 installed at the entrance ofthe MFP 1 (45), the CPU 19 finishes the elimination process (46).

Here, the sheet guided into the MFP 1 is stored in the sheet cassette 4installed in the MFP 1. The sheet stored in the sheet cassette 4, by aninstruction of selection of the sheet cassette from the control panel 5of the MFP 1, is used for image formation of the MFP 1. Further, whennot detecting that the sheet does not pass through the first sensor 16or the second sensor 17 for a predetermined period of time after thesheet supply motor 25 for picking up the sheet from the sheet cassette 4is driven, the CPU 19 displays an occurrence of sheet jamming in theimage elimination apparatus 2 on the control panel 5 installed on theMFP 1 and notifies the sheet jamming to the user. Further, when theimage elimination apparatus is not connected to the MFP 1 and has nodisplay unit, to notify no connection of the image elimination apparatusto the user by a warning sound or a voice is possible.

Further, when a plurality of sheets are set on the sheet supply tray 7,if the heater 14 is repeatedly turned on or off each time, the life spanof the heater is shortened. If the heater 14 is turned off once, thereare possibilities of an occurrence of failure such that until the heaterreaches an appropriate temperature after the heater is turned onthereafter, a long period of time is taken. Therefore, after the heater14 is turned on, until the sheets on the sheet supply tray 7 are allused up, regardless of the possibility of reuse of the sheets, theheater 14 is kept on. And, the sensor installed on the sheet supply tray7 detects that the sheets are all gone and then after confirming thatthe sheets pass through the heater 14, the CPU 19 turns off the heater14.

By use of the aforementioned constitution, the reading for judging thepossibility of reuse of the sheet on which the image is formed isexecuted with high precision, and the reading for checking imageelimination is executed with lower precision, and the same readingportion is used for both readings, so that a small image eliminationapparatus having a high processing speed can be provided.

Next, the second embodiment will be explained. In this embodiment, theexplanation duplicated with the first embodiment will be omitted and thedifferences will be explained. In this embodiment, the image eliminator10 has a number of elimination times recording portion for making apunch hole at a predetermined position of a sheet according to thenumber of elimination times after elimination of an image. The number ofelimination times recording portion records the number of eliminationtimes every image elimination. Hereafter, in the second reading, thereader 9 reads the density of the sheet image and the number of punchholes. FIGS. 6 and 7 show the flow charts of the operations of the imageelimination apparatus in this embodiment, though they are the sameoperations as those at 30 to 37 shown in FIG. 4 of the first embodiment,so that the explanation thereof will be omitted. Hereinafter, theoperations following the second reading will be explained. The secondreading reads whether the image is eliminated or not and the number ofpunch holes. Here, when the sheet image is not eliminated and the CPU 19judges from the status of the punch holes that as a result of comparison(47), the number of elimination times does not reach a predeterminednumber of times (N at 47), the CPU 19 sets the sheet conveying speed tothe first speed which is the same as that at the execution time of thefirst reading (48), then permits the sheet to pass again through theimage eliminator 10, eliminates the image, and records the number ofelimination times. Hereafter, the CPU 19 drives the second flapper 17(41), sets the second speed (47), permits the sheet to pass through thesecond sheet conveying path 18, and executes again the second reading bythe reader 9. In the second reading, the reader 9 reads whether theimage is eliminated or not and reads the number of punch holes. Byreading the number of punch holes, the number of elimination times isjudged (47). When judging that the number of elimination times reachesthe predetermined number of times (Y at 47), the CPU 19 drives the firstflapper 16 (38), in order to abolish the sheet, guides the sheet to thestack box 11, and finishes the elimination process (40). If the CPU 19,from the number of punch holes read simultaneously in the secondreading, judges that the number of elimination times does not reach thepredetermined number of times, the CPU 19 guides the sheet to the MFP 1.

By use of the aforementioned constitution, an image eliminationapparatus for surely eliminating the image of a used sheet, when thenumber of elimination times reaches the predetermined number of times,abolishing the sheet, thereby removing a sheet of a large number ofelimination times and of a deteriorated quality can be provided.

Next, the third embodiment equipped separately with the first reader andsecond reader will be explained.

FIG. 8 is a schematic view of the image elimination apparatus 2 relatingto this embodiment. From the operation of reading the status that thesheet in this embodiment is a judgment material of possibility of use tothe operation of image elimination and the operations after readingwhether the image is eliminated from the sheet or not are almost thesame as those of the first embodiment, so that the explanation will beomitted. The image elimination apparatus 2 of this embodiment is builtin the post-processing device 3 similarly to the first embodiment,includes a sheet supply tray 60, along a sheet conveying path 61, afirst reader 62 and an image eliminator 63, and a second reader 64 onthe downstream side of the image eliminator 63 on the sheet conveyingpath 61 and furthermore has a stack box 65 installed to abolish thesheet which comes off the sheet conveying path 61 and is judged asnonreusable.

Next, the operations will be explained. Firstly, if sheet elimination isinstructed from the control panel of the MFP 1, the CPU 19 turns on aheater 68 and rotates rollers 166. Next, the CPU 19 picks up the sheetsloaded on the sheet supply tray 60 one by one. And, the first reader 62reads the image on the sheet surface and detects the status of creasesof the sheet. Here, when the sheet is judged as nonreusable, the CPU 19drives a flapper 66, guides the sheet to the stack box 65, confirms thatthe sheet passes through a sensor 67, and then finishes the eliminationprocess. On the other hand, while the sheet judged as reusable passesthrough the image eliminator 63, the heater 68 applies heat to the sheetto eliminate the image. While the sheet passing through the imageeliminator 63 passes furthermore through the second reader 64, the CPU19 checks whether the image on the sheet is eliminated or not. Thesecond reading may be executed with lower precision than the firstreading. Therefore, the density of the CCD used may be lowered than thatof a CCD sensor installed in the first reader 62. In the second reading,when that the image is not eliminated is judged, in order to abolish thesheet, the COU 19 drives the flapper 66, guides the sheet to the stackbox 65, confirms that the sheet passes through the sensor 67, and thenfinishes the elimination process. On the other hand, the sheet judgedthat the image is eliminated is supplied to the MFP 1 and theelimination process is finished.

As mentioned above, the first reader 62 and second reader 64 areinstalled separately, thus there is no need to return the sheet again tothe reader after image elimination. Therefore, the labor and time ofreturning the sheet to the reader are saved and there is no need toswitch the sheet conveying speed, so that the image can be eliminatedefficiently from the sheet and the sheet can be supplied quickly to theimage forming apparatus.

In the present invention, furthermore, by use of the fourth embodimentindicated below, the processing efficiency can be improved. In thisembodiment, the arrangement of the readers and image eliminators may bethe same as that of either of the first embodiment and third embodiment,though the first embodiment will be explained as an example.

In this embodiment, when a predetermined number of sheets n to beprocessed first are all almost uniform and reusable, for the residualsheets, the first reading and elimination are executed by conveying at aslightly fast speed. FIGS. 9 and 10 show the flow charts of theoperations of the image elimination apparatus 2 in this embodiment.Firstly, as an initial state, the speed for enabling highly precisereading and sure image elimination and the number of sheets to beprocessed 0 are set (71). Next, the status of the sheets is read by thefirst reader 62 (72) and the possibility of reuse is decided (73). Here,the sheets judged as unusable (N at 73) are abolished (74). At the timeof the first reading, for the first sheet, the first reader 62 reads theposition indicating the highest density on the sheet and the informationon the print condition of the sheet such as the density and stores theinformation in the RAM 22 installed in the apparatus (75, 76). Next,according to the settings of the initial conditions stored beforehand inthe ROM 21, the first reader 62 executes the first reading andelimination of the image on the sheet. Here, if the read sheet isreusable and the print condition of the sheets such as the highestdensity of the first sheet stored in the RAM 22 is almost the same (78),the first reader 62 counts up the number of processed sheets (79). Untilthe counted-up number of processed sheets reaches the predeterminednumber of sheets n, the processing is continued in the state that theconditions such as the sheet conveying speed and the temperature of theheater 14 are kept straight as the initial conditions. When thecounted-up number of processed sheets reaches the predetermined numberof sheets n (80), that the residual sheets stacked on the paper supplytray 7 are all reusable, and the print condition is uniform, and thefirst reading precision for the residual sheets may be lowered smoothly,thus the sheet conveying speed relating to the first reading andelimination is set to a speed faster than the initial speed. Further,from the highest density of the image on the sheet stored in the RAM 22,the CPU 19 obtains a necessary and sufficient temperature to eliminatethe image indicating the highest density and sets the heater 14 to thetemperature (81).

Hereafter, when the first reading (72), elimination (82), and secondreading (83) are continued until the sheets on the paper supply tray 7are all used up under the same conditions and that the sheets are allgone is detected (87), the CPU 19 finishes the process (88). On theother hand, when that between the first sheet and the “n”th sheet, thereis at least one sheet which is not reusable or is different in the sheetstatus is judged, assuming the sheets stacked on the sheet supply tray 7as non-uniform, the process is continued without changing the conditionssuch as the sheet conveying speed and the temperature of the heater 14which are set first. Further, when that the sheet status is reusable anduniform is judged, the first reading may be omitted. Further, when thehighest density of the sheet does not reach a preset value, assuming theimage not to be printed, to turn off the heater 14 and not eliminate theimage is possible. Furthermore, unless the image eliminator 10 changesthe temperature of the heater 14, from the read density of the image onthe sheet, the passing speed of the sheet through the image eliminator10 can be set. Further, when the first sheet to the “n”th sheet arejudged to be almost uniform in the sheet status and the sheets after the“n”th sheet are read with the first reading precision lowered, if thatthe sheet status is different greatly is detected, to execute the firstreading of the sheet under the initial conditions is possible.

In this embodiment, when the first sheet to the “n”th sheet are reusableand the sheet status is almost uniform, in the second reading, only theposition indicating the highest density stored in the RAM 22 is decidedas a reading object and the number of comparison times for checkingwhether the image is eliminated or not can be reduced. Furthermore, toincrease the sheet conveying speed before the sheet reaches the positionindicating the highest density and after reading and improve theprocessing speed is possible.

According to the embodiment aforementioned, when eliminating sheets usedin a conference in a batch, that is, when processing a large quantity ofsheets in almost the same status at a time by the image eliminationapparatus 2, there is no need to read the statuses one by one for allthe sheets. Namely, only by checking only the preset status of the nsheets, the conditions such as the first reading speed and the settemperature of the heater 68 are set, so that the processing time can bereduced. Further, when eliminating the image, applying unnecessary heatto the sheet can be prevented. Therefore, the life span of the sheetscan be lengthened and the power consumption can be reduced.

The present invention can realize furthermore high efficiency of theprocessing by the fifth embodiment indicated below. The fifth embodimentperforms the processes from the first reading to image elimination forall the sheets stacked on a sheet supply tray 98. Thereafter, the secondreading is performed for all the sheets with the image eliminated. FIG.11 is a schematic view of the image elimination apparatus 2 relating tothis embodiment. The constitution of the image elimination apparatus 2does not include the second sheet conveying path as indicated in thefirst embodiment and instead, includes a second flapper 90 and a sheettray 91. Hereinafter, the operation of the fifth embodiment will beexplained. Firstly, the sheets are picked up one by one from the sheetsupply tray 98 and a reader 97 reads whether the sheets are reusable ornot. Next, the sheets are eliminated by a heater 93 of an imageeliminator 92. In this embodiment, the sheets finishing the operationsto image elimination are stacked on the sheet tray 91 by driving thesecond flapper 90. The operations from the first reading to stacking onthe sheet tray 91 via elimination are performed until the sensorinstalled on the sheet supply tray 98 detects that the sheets stacked onthe sheet supply tray 98 are all gone. Further, the sheets judged asnonreusable, similarly to the aforementioned embodiment, are guided to astack box 95. After that the sheets on the sheet supply tray 98 are goneis detected and the first reading of the sheets and image eliminationare finished, until the sheets are conveyed to the sheet tray 91, assoon as sufficient time elapses, the sheet tray 91 slides upward, andthe heating of the heater 93 installed in the image eliminator 92 isfinished. Next, the sheet tray 91 slides from the position where thesheet tray 91 is generally situated when the first reading andelimination are executed up to the position where the sheets can besupplied to a sheet conveying path 94. The sheet conveying speed is setto the second speed, and the sheets are picked up one by one from theslid sheet tray 91 onto the sheet conveying path 94, and the secondreading is executed. Here, whether the image on each sheet is eliminatedeffectively or not is checked and the sheets that the image eliminationcannot be confirmed are guided to the stack box 95.

Further, to install a pickup roller for picking up sheets from the sheettray 91 with the sheet tray 91 fixed unless the sheet tray 91 slides,pick up the sheets stacked on the sheet tray 91 one by one, rotate aroller 96 in the opposite direction to the first reading, permit theroller 96 to pass through the reader 97, and check whether the sheetimage is eliminated or not is possible. Further, in this case, thebranch point to the entrance to the MFP 1 is installed on the upstreamside (above the reader shown in FIG. 11) of the reader 97.

By use of this embodiment, in the case of a large number of processingsheets, only one switching of the first speed and second speed issufficient, thus the processing time can be reduced. Further, at thetime of the second reading, there is no need to turn on the heater 93,so that the power consumption can be reduced.

The present invention can be realized also by the sixth embodimentindicated next. FIGS. 12 to 14 are schematic views showing thisembodiment. In the drawing, the arrows show the passing direction ofsheets. Firstly, the sheet supplied from a sheet supply tray 104 isconveyed at the first speed, and as shown in FIG. 12, a reader 100executes the first reading and detects the status of the sheet, and aheater 102 of an image eliminator 101 is heated, thus the image of thesheet is eliminated. The CPU 19, upon confirmation of passing of thesheet through the image eliminator 101, stops the sheet. And, the CPU 19rotates a roller 103 in the opposite direction, conveys the sheet asshown in FIG. 13, and returns the leading edge of the sheet up to thestart position of the reader 100. Next, the CPU 19 sets the conveyingspeed to the second speed, drives the roller 13 to permit the sheet topass through the reader 100, and executes the second reading in order tocheck whether the image on the sheet is eliminated or not. Here, when atthe time of the first reading, the sheet is reusable and at the time ofthe second reading, the image of the sheet is eliminated on a reusablelevel, the sheet is reusable by the MFP 1, thereby is conveyed to thesheet cassette 4 in the MFP 1. When judging at the time of the firstreading that the sheet is not reusable or when judging at the time ofthe second reading that the image of the sheet is not eliminated on thereusable level, the CPU 19 conveys and abolishes the sheet at a stackbox 111. Further, as shown in FIG. 14, when conveying the sheet in theopposite direction to the direction at the time of execution of thefirst reading and elimination, the elimination of the image may bechecked. In this way, a conveying path is installed from above to theMFP 1 as shown in FIG. 14, thus the number of sheet conveying times canbe reduced and the processing speed can be increased. In thisembodiment, there is no need to install the second sheet conveying pathas in the first embodiment, so that the possibility of reuse of usedsheets can be executed at high precision, and the processing speed canbe increased, and furthermore, the image elimination apparatus can beminiaturized.

As mentioned above, according to the present invention, an imageelimination apparatus and an image eliminating method of judging thepossibility of reuse of used sheets at high precision and at a fastprocessing speed can be provided.

What is claimed is:
 1. An image elimination apparatus comprising: asheet supply unit configured to supply a sheet on which an image isformed; a reader configured to read a sheet supplied thereto, saidreader disposed along a first conveying path; an image eliminatorconfigured to eliminate an image formed on a sheet supplied thereto; astacker configured to stack sheets that are not reusable; a memoryconfigured to store a first reference value based on which a reusabilityof the sheet is judged and a second reference value, which is differentfrom the first reference value, based on which it is judged whether theimage formed on the sheet has been eliminated or not; a second sheetconveying path that branches from the first sheet conveying path at adownstream side of said reader along a sheet conveying direction, andjoins said first sheet conveying path at an upstream side of said readeralong the sheet conveying direction; a separating unit configured toswitch a conveying path of the sheet between a path to the stacker and apath to said second sheet conveying path, and disposed at a positionwhere the second sheet conveying path branches from the first sheetconveying path; and a controller configured to judge the reusability ofthe sheet based on the first reference value and a first reading, whichis performed by said reader at a first time and at a first readingspeed, and to judge whether the image formed on the sheet has beeneliminated or not based on the second reference value and a secondreading, which is performed by said reader at a second time and at asecond reading speed that is faster than the first reading speed;wherein, in the case the sheet is judged not to be reusable, the sheetis ejected to said stacker before the second reading, and in the casethe sheet is judged to be reusable and said controller judges that theimage has not been eliminated, the sheet is conveyed towards the path tothe stacker.
 2. The apparatus according to claim 1, wherein said imageeliminator is configured to eliminate the image by heat.
 3. Theapparatus according to claim 1, wherein said controller judgesreusability of the sheet based on at least one of a depth of a crease ofthe sheet or a corner fold.
 4. The apparatus according to claim 1,wherein said controller reads a printing rate of the sheet beforeeliminating and judges whether the sheet is reusable based on the firstreference value.
 5. The apparatus according to claim 1, wherein thereading result indicates a position on the sheet that is of the highestdensity among the image formed on the sheet and the controller judgeswhether the image is eliminated at the position based on the secondreading result.
 6. The apparatus according to claim 1, wherein thecontroller controls the reader so that a reading precision of the firstreading is higher than a reading precision of the second reading.
 7. Theapparatus according to claim 1, further comprising another separatingunit, wherein said controller conveys the sheet toward a sheet cassetteof an image forming apparatus for feeding the paper therein via saidanother separating unit when the controller judges that the image iseliminated.
 8. An image elimination apparatus comprising: a sheet supplyunit configured to supply a sheet on which an image is formed; a readerconfigured to read a sheet supplied thereto, said reader disposed alonga first conveying path; an image eliminator configured to eliminate animage formed on a sheet supplied thereto by heat, the image eliminatorhaving a heater; a stacker configured to stack sheets that are notreusable; a memory configured to store a first reference value based onwhich a reusability of the sheet is judged and a second reference value,which is different from the first reference value, based on which it isjudged whether the image formed on the sheet has been eliminated or not;a second sheet conveying path that branches from the first sheetconveying path at a downstream side of said reader along a sheetconveying direction, and joins said first sheet conveying path at anupstream side of said reader along the sheet conveying direction; aseparating unit configured to switch a conveying path of the sheetbetween a path to the stacker and a path to said second sheet conveyingpath, and disposed at a position where the second sheet conveying pathbranches from the first sheet conveying path; and a controllerconfigured to judge the reusability of the sheet based on the firstreference value and a first reading, which is performed by said readerat a first time, and to judge whether the image formed on the sheet hasbeen eliminated or not based on the second reference value and a secondreading, which is performed by said reader at a second time; wherein, inthe case the sheet is judged not to be reusable, the sheet is ejected tosaid stacker before the second reading, and in the case the sheet isjudged to be reusable and said controller judges that the image has notbeen eliminated, the sheet is conveyed towards the path to the stacker,and wherein said supply unit is disposed above said image eliminator,and said reader and said stacker are disposed under said imageeliminator in a vertical direction of the apparatus.
 9. An image formingapparatus comprising: a sheet supply unit configured to supply a sheeton which an image is formed; a reader configured to read a sheetsupplied thereto, said reader disposed along a first conveying path; animage eliminator configured to eliminate an image formed on a sheetsupplied thereto; a stacker configured to stack sheets that are notreusable; a memory configured to store a first reference value based onwhich a reusability of the sheet is judged and a second reference value,which is different from the first reference value, based on which it isjudged whether the image formed on the sheet has been eliminated or not;a second sheet conveying path that branches from the first sheetconveying path at a downstream side of said reader along a sheetconveying direction, and joins said first sheet conveying path at anupstream side of said reader along the sheet conveying direction; aseparating unit configured to switch a conveying path of the sheetbetween a path to the stacker and a path to said second sheet conveyingpath, and disposed at a position where the second sheet conveying pathbranches from the first sheet conveying path; a controller configured tojudge the reusability of the sheet based on the first reference valueand a first reading, which is performed by said reader at a first timeand at a first reading speed, and to judge whether the image formed onthe sheet has been eliminated or not based on the second reference valueand a second reading, which is performed by said reader at a second timeand at a second reading speed that is faster than the first readingspeed; wherein, in the case the sheet is judged not to be reusable, thesheet is ejected to said stacker before the second reading, and in thecase the sheet is judged to be reusable and said controller judges thatthe image has not been eliminated, the sheet is conveyed towards thepath to the stacker; and said controller configured to convey the sheetto a discharge port, when the image is eliminated; and an image formingunit which forms an image on the sheet which is conveyed from thedischarge port.
 10. An image elimination method comprising: supplying asheet on which an image is formed; reading the sheet a first time at afirst reading speed; judging a reusability of the sheet based on thereading at the first time and a first reference value; if the sheet isjudged not to be reusable, conveying the sheet to a stacker; and if thesheet is judged to be reusable, conveying the sheet to an imageeliminator to eliminate the image formed on the sheet, reading the sheeta second time at a second reading speed that is faster than the firstreading speed, judging whether the image formed on the sheet has beeneliminated or not based on the reading at the second time and a secondreference value that is different from the first reference value, andconveying the sheet to the stacker if the image is judged to not havebeen eliminated.
 11. The method according to claim 10, wherein judgingreusability of the sheet is based on at least one of a depth of a creaseof the sheet or a corner fold.
 12. The method according to claim 10,wherein a printing rate of the sheet is read before eliminating and thejudgment whether the sheet is reusable is based on the first referencevalue.
 13. The method according to claim 10, wherein the reading resultindicates a position on the sheet that is of the highest density amongthe image formed on the sheet and the judgment whether the image iseliminated at the position is based on the second reading result. 14.The method according to claim 10, wherein the reader is controlled sothat a speed of the first reading is slower than a speed of the secondreading and a reading precision of the first reading is higher than areading precision of the second reading.
 15. The apparatus according toclaim 1, wherein said controller to judge whether the image iseliminated or not by judging a pixel, which has more than apredetermined density, on the sheet where the image is eliminated,exists or not at the second reading.
 16. The apparatus according toclaim 1, wherein said controller performs the second reading at saidreader, after the sheet, which is judged as reusable at the firstreading, is conveyed to said second sheet conveying path.
 17. Theapparatus according to claim 1, wherein said controller performs thesecond reading toward the sheet, which is conducted to be eliminated bysaid image eliminator after the first reading, by said reader.